EDAC: Handle error path in edac_mc_sysfs_init() properly

Make sure proper deregistration happens on all error paths in
edac_mc_sysfs_init.

Signed-off-by: Denis Kirjanov <kirjanov@gmail.com>
[ Boris: cleanup and concretize commit message ]
Signed-off-by: Borislav Petkov <bp@alien8.de>